1. Field of the Invention
The present invention relates to a heat transferable label and improved release composition therefor.
2. Description of the Prior Art
Prior art heat transferable labels for imprinting designs onto an article typically involve decorative laminates consisting of a paper base sheet or web coated with a wax or polymeric release layer over which a design is imprinted in ink.
U.S. Pat. No. 3,616,015 is illustrative of the prior art. In U.S. Pat. No. 3,616,015 a label-carrying web such as a paper sheet includes a heat transferable label composed of a wax release layer affixed to a surface of the paper sheet and an ink design layer superimposed onto the wax release layer. In the heat transfer labelling process for imprinting designs onto articles, the label-carrying web is subjected to heat, and the laminate is pressed onto an article with the ink design layer making direct contact with the article. As the web or paper sheet is subjected to heat, the wax layer begins to melt so that the paper sheet can be released from the wax layer. After transfer of the design to the article, the paper sheet is immediately removed, leaving the design firmly affixed to the surface with the wax layer exposed to the environment. The wax release layer should not only permit release of the transferable label from the web upon application of heat to the web but also form a clear, protective layer over the transferred ink design.
This commonly assigned patent discloses a wax release coating containing a modified montan wax which has been oxidized, esterified, and partially saponified. Paraffin wax, microcrystalline wax, and a rosin ester are included in the wax blend along with the montan wax. The release formulation is prepared without the inclusion of a solvent. It is, therefore, prepared as a hot melt mixture and is applied as a hot melt onto the carrier. In order to attain improved clarity of the transferred ink design, the transferred wax coating over the ink design is subjected to additional heat processing after the label has been transferred onto the article. The additional processing involves postflaming, wherein the transferred wax coating is subjected to jets of high temperature gas either as direct gas flame or as hot air jets at temperatures of about 300.degree. F. to 400.degree. F. for a period of time sufficient to remelt the wax coating without substantially heating the bottle. Upon cooling of the remelted wax coating through use of ambient or forced cooled air, the cooled wax layer solidifies to form a clear, smooth, glossy, protective coating over the transferred ink design. After the design is transferred onto an article, the transferred release layer which now forms a protective coat over the design cannot be subjected to hot water for significant duration since this would tend to melt the release and consequently dull the transferred release. U.S. Pat. No. 3,616,015 is herein incorporated by reference.
U.S. Pat. No. 3,516,842 discloses a heat transfer label which is heat transferable from a paper carrier sheet to a plastic bottle. This reference discloses a wax-like release layer which may be composed of any one of three compositions: (I) the release disclosed may be composed of a slightly oxidized, low molecular weight polyethylene wax (col. 2, line 65 to col. 3, line 3); or (II) the release layer may be of an unoxidized hard wax, which wax after deposition on the paper carrier has been subjected to corona discharge (col. 3, lines 4-13); or (III) the release layer may be a blend of ethylene-vinyl acetate (EVA) copolymer and a paraffin wax (col. 3, lines 14-21). These release compositions do not provide sufficient adhesion to uniformly bond to the ink design layer or intermediate lacquer coating which may be included between the release layer and ink design layer. The above release compositions do not exhibit the required high degree of film integrity during the heat transfer of the print image to the receiving article. Lack of sufficient film integrity results in shrinkage of the release layer during transfer and distortion of the transferred image.
U.S. Pat. No. 2,989,413 discloses a heat transferable laminate employing a release layer composed of an unoxidized Fisher-Tropsch wax. The unoxidized wax is employed as a release layer without incorporation of other wax or resin additive. The use of unoxidized waxes alone in release coatings for heat transferable laminates has proved to be unsatisfactory. The unoxidized wax alone does not exhibit sufficient adhesion to uniformly bond to the ink design or intermediate lacquer coating to the release surface.
U.S. Pat. No. 2,990,311 discloses a heat transferable decal having a release transfer layer composed of a mixture of a crystalline wax and a synthetic thermoplastic film-forming resin, principally an organic linear thermoplastic film-forming resin which is substantially water insoluble. The degree of compatibility of the resin and wax is controlled through selection and ratio of the components to give heat transfers of either the hot-peel or cold-peel type. In the hot-peel transfer, the decal will adhere and release from the backing only immediately after application while the decal is still hot. In the cold-peel transfer, the transferred decal will adhere to the receiving surface when hot but will only release and transfer by peeling away the backing after the transfer has cooled. In either type of transfer, this reference teaches that resins and waxes (the latter being used for the release layer) should be mutually incompatible or insoluble at temperatures below the melting temperature of the wax such that the molten wax, upon cooling, will actually crystallize separately and distinctly from the resin.
Suitable resins specifically disclosed are polyvinyl acetate, polyethyl acrylate, polymethyl acrylate, polyethyl methacrylate, polypropyl methacrylate, polybutyl methacrylate, styrenebutadiene, acrylonitrile-butadiene, polychloroprene rubbers, polyvinyl butyral, ethyl cellulose, and polyvinyl acetate vinyl stearate copolymer (col. 5, lines 38-44). The reference teaches that the wax component should be a material which derives its crystallinity mainly from the presence of long hydrocarbon chains.
Specific waxes disclosed as suitable are beeswax, candelilla wax, carnauba wax, hydrogentated castor oil, montan wax, paraffin wax, low molecular weight polyethylene, oxidized microcrystalline wax, and hard wax or derivatives thereof obtained from the Fischer-Tropsch synthesis. (col. 5, lines 45-56). This reference does not disclose applicant's formulation for the release layer nor does it contemplate the advantages which applicant has derived from such formulation.
U.S. Pat. No. 2,862,832 discloses a heat transferable decal having a release layer composed of an oxidized wax. The disclosure is directed principally to defining the type of wax found to provide suitable release of the decal from the carrier web upon application of heat. The wax disclosed in this reference is an oxidized wax obtained as the reaction product of the oxidation of hard, high melting, aliphatic, hydrocarbon waxes. The oxidized waxes are defined as the oxidation products of both natural and synthetic hydrocarbon waxes such as petroleum waxes, low molecular weight polyethylene and waxes obtained from the Fisher-Tropsch synthesis. Suitable waxes may include oxidized microcrystalline wax or the esterification product of an oxidized hydrocarbon wax. The oxidized waxes are disclosed as those having melting points between about 50.degree. C. and 110.degree. C., saponification values between about 25 and 100, acid values between about 5 and 40, and penetrometer hardness (ASTM D5-52) below about 51 as measured with 100 grams for 5 seconds at 25.degree. C. This reference does not disclose applicant's release formulation nor does it recognize or contemplate the advantages obtained from such formulation.
U.S. Pat. No. 3,616,176 discloses a heat transfer laminate of a type related to that disclosed in U.S. Pat. No. 3,616,015. In U.S. Pat. No. 3,616,176 the laminate is composed of a base sheet, with a polyamide layer covering the base sheet and a decorative ink layer covering the polyamide layer. Sufficient heat is applied to the laminate to heat the polyamide layer at or above a softening point, and the laminate is then pressed onto the surface of an article with the decorative ink layer coming into direct contact. Upon withdrawal of the heat source, the polyamide layer cools to a temperature below the softening point and the base sheet is removed. The decorative layer becomes fused or heat sealed to the article. The polyamide layer in this disclosure functions as a release coating which allows transfer of the decorative layer onto an article and upon cooling serves as a protective coating layer over the transferred decorative layer. The use of a polyamide release coating has the principal disadvantage in that there is a significant tendency for the polyamide to form a noticeable halo around the transferred decorative layer. Also, the polyamide layer even when subjected to additional processing such as postflaming does not form a sufficiently clear coating that would aesthetically permit heat transfer labelling onto clear articles or bottles.
U.S. patent application Ser. No. 06/501454 filed 06/06/83, now abandoned entitled Heat Transferable Laminate, commonly assigned with the present application, discloses a heat transferable release formulation containing, inter alia, a montan wax and an ethylene-vinyl acetate copolymer binder. The release formulation disclosed in this application is prepared and applied to the carrier web as a hot melt; i.e. without the use of solvent and is, therefore, of a different type release than the solvent-based wax release of the present application.
U.S. patent application Ser. No. 06/544024 filed 10/20/83, now U.S. Pat. No. 4,536,434 entitled Heat Transferable Laminate, commonly assigned with the present invention, contains relevant disclosure pertaining to the method of transferring the laminate to a receiving article and postheating the transferred laminate on the article. The improved heat transferable release disclosed therein is of a markedly different type than the formulation of the present invention in that it does not employ a montan wax and it is prepared and applied to the carrier web as a hot melt; i.e. the release formulation does not contain a solvent during its application onto the carrier web.
Accordingly, it is an object of the present invention to provide an improved release for heat transferable laminates wherein the release is a solvent-based wax formulation.
It is an object of the invention that the release coating prior to drying has a low gel point approaching ambient temperature.
It is another object that the release coating be heat transferable so that it forms a clear, hard, glossy protective coating exhibiting improved scuff resistance.
It is an important objective that the release coating after transfer withstand exposure to hot water.